16 Colorado Experiment Station 
orifice to bottom of the box; an appreciably greater head due to the depth 
of water pouring over the spill-crest. 
Some of the Miner’s Inch measuring devices are well adapted to the 
conditions under which they are used. They are especially applicable to 
the measurement of small flows of water and when used in connection 
with a spill-box they act somewhat as a proportional divider. They are 
not well suited to the rotation method of delivery of water where large 
quantities are delivered for short periods, and they will not deliver a 
flow much in excess of their normal capacity. These measuring devices 
are often unjustly condemned, for the fault is not with the orifice struc¬ 
tures as much as with the unit of measurement used, the Inch, whether 
it be called Miner’s, Statute, Customary, or Parmer’s Inch. These orifices 
are reasonably accurate in their measurement of water, but they should 
be calibrated or built according to plans which will give a known dis¬ 
charge, and this discharge should be expressed in cubic feet per second 
or some other equally definite quantity. 
UNITS OF MEASURE. 
The Cubic Foot Per Second, called second-foot, is a unit of measure 
for flowing water. When a stream discharges 1 cubic foot of water in 
one second, there is a second-foot flow. 
The Acre-Foot is a unit of measure for standing water, and is that 
volume which will cover one acre one foot deep. An acre-inch is one- 
twelfth of an acre-foot, or the volume which will cover one acre to a 
depth of one inch. 
The Miner’s Inch is unsatisfactory and rapidly losing favor as a 
unit for measuring water, because it is not a definite quantity. It varies 
with the conditions under which it is used, and is therefore being replaced 
by the second-foot. In several of the Western states the Miner’s Inch 
has been defined by law as being a certain fractional part of a second- 
foot, and these values are given in the accompanying table of Hydraulic 
Equivalents. 
TABLE OP HYDRAULIC EQUIVALENTS. 
1 cubic foot equals 7.48 gallons, or approximately 7 V 2 gallons. 
1 cubic foot of water weighs approximately 62 y 2 pounds. 
1 cubic foot per second equals 4 48.8 3 gallons per minute, or ap¬ 
proximately 4 50 gallons per minute. 
1 cubic foot per second flowing for 1 hour equals approximately 1 
acre-inch. 
1 cubic foot per second flowing for 12 hours equals approximately 
1 acre-foot. 
1 cubic foot per second flowing for 24 hours equals approximately 
2 acre-feet. 
1 acre foot equals 43,560 cubic feet, equals 325,851 gallons. 
1,000,000 cubic feet (1 million cu. ft.) equals 22.95 acre-feet. 
In California, Nevada, and Montana, 1 Miner’s Inch (Statutory Inch) 
equals 1-40 of 1 cubic foot per second. 
In Utah, Idaho, Arizona, and New Mexico, 1 Miner’s Inch (Statutory 
Inch) equals 1-50 of one cubic foot per second. 
In Colorado it has been generally assumed that 1 Miner’s Inch (Stat¬ 
utory Inch) equals 1-38.4 of one cubic foot per second. 
